Getting some errors on setActionBar()

Question

So i'm having some trouble with my code with this error i'm using androidx and i think the problem is because of dat. for being honest i don't know how to change to old version android

so the error is this

error: incompatible types: androidx.appcompat.widget.Toolbar cannot be converted to android.widget.Toolbar

I already tried to import android.support.v7.wigdet.Toolbar did not work :(

MainActivity.Java

import androidx.appcompat.app.AppCompatActivity;
import androidx.appcompat.widget.Toolbar;



import android.os.Bundle;

public class MainActivity extends AppCompatActivity {

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);

        Toolbar toolbar = findViewById(R.id.toolbar);
        setActionBar(toolbar);
    }

nav_header.xml

activity_main.xml

Build.gradle

Update error when run

E/AndroidRuntime: FATAL EXCEPTION: main
    Process: com.example.readytogo, PID: 8403
    java.lang.RuntimeException: Unable to start activity ComponentInfo{com.example.readytogo/com.example.readytogo.MainActivity}: android.view.InflateException: Binary XML file line #26 in com.example.readytogo:layout/activity_main: Binary XML file line #26 in com.example.readytogo:layout/activity_main: Error inflating class fragment
        at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:3260)
        at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:3396)
        at android.app.servertransaction.LaunchActivityItem.execute(LaunchActivityItem.java:83)
        at android.app.servertransaction.TransactionExecutor.executeCallbacks(TransactionExecutor.java:135)
        at android.app.servertransaction.TransactionExecutor.execute(TransactionExecutor.java:95)
        at android.app.ActivityThread$H.handleMessage(ActivityThread.java:2009)
        at android.os.Handler.dispatchMessage(Handler.java:107)
        at android.os.Looper.loop(Looper.java:214)
        at android.app.ActivityThread.main(ActivityThread.java:7319)
        at java.lang.reflect.Method.invoke(Native Method)
        at com.android.internal.os.RuntimeInit$MethodAndArgsCaller.run(RuntimeInit.java:492)
        at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:934)
     Caused by: android.view.InflateException: Binary XML file line #26 in com.example.readytogo:layout/activity_main: Binary XML file line #26 in com.example.readytogo:layout/activity_main: Error inflating class fragment
     Caused by: android.view.InflateException: Binary XML file line #26 in com.example.readytogo:layout/activity_main: Error inflating class fragment
     Caused by: java.lang.NullPointerException
        at java.lang.VMClassLoader.findLoadedClass(Native Method)
        at java.lang.ClassLoader.findLoadedClass(ClassLoader.java:738)
        at java.lang.ClassLoader.loadClass(ClassLoader.java:363)
        at java.lang.ClassLoader.loadClass(ClassLoader.java:312)
        at android.app.Fragment.instantiate(Fragment.java:536)
        at android.app.FragmentContainer.instantiate(FragmentContainer.java:53)
        at android.app.FragmentManagerImpl.onCreateView(FragmentManager.java:3553)
        at android.app.FragmentController.onCreateView(FragmentController.java:104)
        at android.app.Activity.onCreateView(Activity.java:6929)
        at androidx.fragment.app.FragmentActivity.onCreateView(FragmentActivity.java:326)
        at android.view.LayoutInflater.tryCreateView(LayoutInflater.java:1069)
        at android.view.LayoutInflater.createViewFromTag(LayoutInflater.java:997)
        at android.view.LayoutInflater.createViewFromTag(LayoutInflater.java:961)
        at android.view.LayoutInflater.rInflate(LayoutInflater.java:1123)
        at android.view.LayoutInflater.rInflateChildren(LayoutInflater.java:1084)
        at android.view.LayoutInflater.rInflate(LayoutInflater.java:1126)
        at android.view.LayoutInflater.rInflateChildren(LayoutInflater.java:1084)
        at android.view.LayoutInflater.inflate(LayoutInflater.java:682)
        at android.view.LayoutInflater.inflate(LayoutInflater.java:534)
        at android.view.LayoutInflater.inflate(LayoutInflater.java:481)
        at androidx.appcompat.app.AppCompatDelegateImpl.setContentView(AppCompatDelegateImpl.java:470)
        at androidx.appcompat.app.AppCompatActivity.setContentView(AppCompatActivity.java:141)
        at com.example.readytogo.MainActivity.onCreate(MainActivity.java:16)
        at android.app.Activity.performCreate(Activity.java:7783)
        at android.app.Activity.performCreate(Activity.java:7772)
        at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1299)
        at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:3235)
        at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:3396)
        at android.app.servertransaction.LaunchActivityItem.execute(LaunchActivityItem.java:83)
        at android.app.servertransaction.TransactionExecutor.executeCallbacks(TransactionExecutor.java:135)
        at android.app.servertransaction.TransactionExecutor.execute(TransactionExecutor.java:95)
        at android.app.ActivityThread$H.handleMessage(ActivityThread.java:2009)
E/AndroidRuntime:     at android.os.Handler.dispatchMessage(Handler.java:107)
        at android.os.Looper.loop(Looper.java:214)
        at android.app.ActivityThread.main(ActivityThread.java:7319)
        at java.lang.reflect.Method.invoke(Native Method)
        at com.android.internal.os.RuntimeInit$MethodAndArgsCaller.run(RuntimeInit.java:492)
        at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:934)

Answer 1

Try this

import androidx.appcompat.app.AppCompatActivity;
import androidx.appcompat.widget.Toolbar;



import android.os.Bundle;

public class MainActivity extends AppCompatActivity {

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);

        Toolbar toolbar = findViewById(R.id.toolbar);
        setSupportActionBar(toolbar);
    }
}

As you are extending from AppComatActivity instead of Activity, so you have to use setSupportActionBar instead of setActionBar.

IN your xml Toolbar is also missing, you need to add toolbar in your activity xml like

    <androidx.appcompat.widget.Toolbar
    android:id="@+id/toolbar"
    android:layout_width="match_parent"
    android:layout_height="wrap_content"
    app:titleTextAppearance="@style/ToolBarStyle" />